C++ – Difference Between Functors and Functions

In C++, we have multiple options to operate over the data like in the case where we can use functions and functors. Although both seem to be similar in a few ways but have multiple differences between them. Let’s check the differences between functions and functors in C++.

What are functions?

Functions are pieces of code that can be called from any other part of a program. They are a way of organizing code so that it is reusable, and can be used to perform a specific set of operations. Functions can be defined in any programming language and are typically used to encapsulate a set of instructions that can be called multiple times.

Example:

C++

#include <iostream>
using namespace std;

// Function definition
int add(int a, int b)
{
   int c = a + b;
   return c;
}

// Driver code
int main()
{
   int a = 5, b = 6;
   int c = add(a, b);
   cout << c;
   return 0;
}

Output

11

What are functors?

Functors, also known as function objects, are objects that behave like functions. They are a type of object that can be treated like a function and can be used to encapsulate a set of instructions. They are similar to functions in that they can be used to encapsulate a set of operations, but they are different in that they can store states and can be used in more complex ways.

Example:

C++

#include <iostream>
using namespace std;

// Functor definition
struct Add {
    // Data members
    int a;

    // Constructor
    Add(int a)
        : a(a)
    {
    }

    // Function call operator
    int operator()(int b) { return a + b; }
};

// Driver code
int main()
{
    Add add(5);
    int c = add(6);
    cout << c;
    return 0;
}

Output

11

Difference between functions and functors

Functors	Functions
Functors are objects that can be called like functions	Functions are blocks of code that can be called by their name
They can be created by defining the function call operator (operator())	They are created by declaring a function with a specific name and syntax
They can store state and retain data between function calls	Functions do not store state and do not retain data between calls
They can be overloaded and customized to perform different tasks	Functions cannot be overloaded and must have a fixed signature
They can be passed as arguments to other functions or returned as results	Functions can only be passed as arguments or returned as results
They can have different types of arguments and return values	Functions must have fixed types of arguments and return values
They are slower to execute than functions due to their added complexity	Functions are faster to execute due to their simplicity